In a network formed by a plurality of nodes, various approaches may be followed for placing the nodes on  standby in order to reduce effectively their electrical power consumption. It is possible for example to place the receiver means of the nodes in sleep mode in periods during which the latter do not transmit or receive data to or from other nodes. Thus the nodes can transmit or receive data only during their waking periods. These waking periods are generally not synchronized between the nodes. It is thus understandable that the choice of a channel access protocol adapted to these constraints proves to be of particular importance when it is a matter of economizing on the energy resources available at each node of the network.
In particular, channel access protocols known as preamble sampling protocols are based on the principle of transmission of a preamble on a channel by a transmitter node having data to transmit to a receiver node. Periodically, and for a brief period, the receiver means of the receiver node are activated, in an asynchronous manner relative to those of the other nodes. The receiver node then listens to the channel to determine if a preamble is being transmitted. The receiver node typically listens to the end of the preamble to access the data. The nodes of the same network having the same channel listening period, the transmitter node sends a preamble for at least as long as the duration of this listening period. All the nodes in the vicinity of the transmitter node are thus awakened by the preamble sent by the transmitter node, which induces an unnecessary consumption of energy. The transmitter node may also insert data into the preamble to enable the receiver node to determine if said preamble concerns it, if data is going to be transmitted to it, and when that transmission will take place. Thus the receiver node may manage the sleeping state of its receiver means accordingly.
Preamble sampling channel access protocols are well suited to sensor networks, characterized by a low data rate. The energy resources of the sensors generally being limited, such management of access to the channel enables significant reductions in energy consumption to be observed, resulting from periodically placing the receiver means of the nodes in the sleeping state. These savings are all the more sensitive given that the traffic generated by such sensors is typically sporadic.
Furthermore, the architecture of sensor networks is typically built around sink nodes responsible for collecting data transmitted by groups of sensor nodes. Also, a significant proportion of the data transmitted over the network converges towards the sink nodes.
Now, known preamble sampling channel access protocols provide for the sending of a preamble by each sensor node seeking to transmit data to one of the sink nodes. When a large number of sensor nodes have data to transmit over a short time period, a large number of preambles are therefore also transmitted. On the one hand, this behavior proves somewhat unsatisfactory from the energy point of view, transmission of each preamble necessitating the consumption by the sensor nodes of a quantity of energy. On the other hand, the risk of collision on access to the channel during this period is notably increased.
There therefore exists a need to transmit data from a plurality of transmitter nodes over a channel to at least one receiver node, minimizing the electrical power consumption of the various transmitter nodes and reducing the risk of collision on access to the channel by the transmitter nodes.